During cyclic polarization of a high entropy alloy in 3.5 wt.% NaCl solution, the pitting potential (at which the current density increases suddenly) was more negative than the potential at which the reverse scan curve intersects the forward scan curve (protection or re-passivation potential). in other words, the reverse polarization part does not intersect with the forward scan part at the passive region of the curve. What is the interpretation of this issue in relation to the degree of resistance to localized corrosion? It should be noted that In the microscopic images of the surface of the samples after corrosion, large pits can be seen.
Yes, the pitting potential can be lower than the re-passivation potential in a cyclic polarization curve. In some cases, a material may exhibit pitting corrosion upon initial exposure to an aggressive environment, leading to a lower pitting potential. However, once the surface passivates, the re-passivation potential may be higher because the newly formed passive film provides a protective barrier against further corrosion. However, you should repeat the test at least three times to confirm the same trend. You can find some literature on Al alloys that show similar results.
Dear Dr. Mohabbat Amirnejad ,
I suggest you to have a look at the following, interesting paper:
- Interpretation of Cyclic Potentiodynamic Polarization Test Results
for Study of Corrosion Behavior of Metals: A Review
S. Esmailzadeh, M. Aliofkhazraei, and H. Sarlak
Protection of Metals and Physical Chemistry of Surfaces, Vol. 54, No. 5, pp. 976–989 (2018)
Available at: https://link.springer.com/article/10.1134/S207020511805026X where is possible download the pdf
and at Gamry Application Note:
- “Potentiodynamic and Cyclic Polarization Scans”, available at:
https://www.gamry.com/application-notes/corrosion-coatings/potentiodynamic-cyclic-polarization/
My best regards, Pierluigi Traverso.
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